1. Field of the Invention
The present invention relates to a composite lens having a resin lens provided on a base lens. In particular, the present invention relates to a composite lens having a resin marker that enables easy alignment of a resin when the resin lens is produced on the base lens.
2. Description of the Related Art
An optical device, such as a digital camera and a portable cellular phone, uses various lenses. However, an aberration arises in an image converged by a spherical lens; hence, the image becomes blurred for reasons of the aberration. Methods, such as a method employing a plurality of lenses with different refractive indices, are available for preventing occurrence of an aberration. However, employment of a large number of lenses is contrary to the need for a reduction in the weight of the optical device. Accordingly, a resin lens having an aspheric shape is produced on the surface of the spherical lens, so as to produce a composite lens functioning as an aspheric lens. By employing the composite lens in the optical device, lightweight and compact optical device whose aberration is corrected is put into practical use.
FIG. 4 illustrates a method for manufacturing a related-art composite lens (see Patent Document 1). As shown in FIG. 4A, under the manufacturing method, firstly resin 42a, such as an UV curable resin or a thermosetting resin, is placed on an aspheric transfer surface of a mold 43. Next, an optical axis of a base lens 41, such as a spherical lens, and a center axis of the mold are aligned to each other, and the resin 42a is pressed by the base lens 41, thereby molding the resin 42a in conformance with the aspheric shape of the transfer surface of the mold 43. Subsequently, as shown in FIG. 4B, the resin is hardened upon exposure to UV radiation or heating according to the type of the resin 42a, thereby producing a resin lens 42 on the base lens 41. Thus, a composite lens, such as that shown in FIG. 4C, can be manufactured. For instance, as shown in FIG. 4D, the thus-manufactured composite lens 44 is attached to a camera cone 45 of the optical device, and an objective-side of the composite lens is supported by an annular holder 45a. The opposite side of the composite lens is fastened to the camera cone 45 by bonding or thermal caulking 46.
A plastic lens or a glass lens is prepared as a base lens used for manufacturing a composite lens. Next, a resin lens is produced on the base lens. However, in order to ensure optical performance of the composite lens, it is important to accurately coincide an optical axis of the base lens and an optical axis of the resin lens with each other, and it is necessary to accurately align the base lens to the mold. FIG. 5 is a view showing a method for producing a resin lens 52 by use of a related-art mold 53. FIG. 5A is a view showing a method for aligning the base lens 51 to the mold 53, and FIG. 5B is a cross-sectional view of the composite lens 54 formed by such a method. As shown in FIG. 5A, under a related-art alignment method, a base material marker 59, which is an annular recess or an annular protuberance, is first provided along an edge of the base lens, and a resin marker 58 having a curvature is formed in the center of a mold surface of the mold 53.
Subsequently, a composite lens for reference purpose is produced, and the degree of alignment between the base marker 59 and the resin marker 58 is measured by a measuring microscope, thereby measuring the degree of alignment between the optical axis of the base lens 51 and the optical axis of the resin lens 52. Next, a relative position between the mold 53 and a base material holding member 55 achieved in a horizontal direction (in a direction perpendicular to the optical axis) is adjusted so as to offset a deviation in the degree of alignment. Subsequently, a composite lens for reference purpose is again produced; the degree of alignment between the base marker 59 and the resin marker 58 of the thus-manufactured composite lens is measured; the degree of alignment between the optical axis of the base lens 51 and the optical axis of the resin lens 52 is measured; and the relative position is subsequently adjusted. When the degree of alignment falls within a desired range through repetition of such feedback operation, alignment of the mold 53 to the base material holding member 55 is completed, and mass-production of a composite lens is commenced. Moreover, even in connection with mass-produced composite lenses, the degree of alignment between the base marker 59 and the resin marker 58 is measured, and misaligned defective resin lenses are sorted out.
In the meantime, there is also a method for utilizing a contour of the base lens 51 as a marker without additional provision of the base material marker 59 during adjustment of the horizontal position of the base lens 51 and the horizontal position of the resin lens 52. The method is for measuring the degree of alignment between the contour of the base lens 51 and the resin marker 58 by means of the measuring microscope, thereby measuring the degree of alignment between the optical axis of the base lens 51 and the optical axis of the resin lens 52 and aligning the mold 53 to the base material holding member 55 on the basis of a resultant measurement value.
However, the resin marker 58 formed in the center of the mold surface used for aligning an optical axis A of the base lens 51 to the mold 53 is present within an optically effective diameter. Hence, from the viewpoint of assurance of optical performance of the composite lens 54, the resin marker 58 must be sufficiently reduced. Since the resin marker 58 has a curvature, a contrast is not clear when the marker is viewed from the direction of the optical axis A. Therefore, the resin marker 58 is not easily seen at time of alignment, which poses a problem of difficulty in measurement of the degree of alignment. There is also a method for placing an annular indentation (not shown) in a neighborhood 58a of an outer circumference of the mold surface rather than in the center of the mold surface and transferring an annular protuberance (not shown) as a resin marker to the neighborhood 58b of the outer circumference of the resin lens 52. (The method will be hereunder called “related-art example 2”) However, as shown in FIG. 5A, the annular indentation formed in the neighborhood 58a of the outer circumference of the mold surface is at a positionally-elevated location in the mold 53; hence, there may be the case where the annular indentation is not sufficiently filled with resin. Insufficient charging of resin makes it difficult to produce the resin marker in a desired shape, which in turn raises a problem of a failure to use the annular protuberance as the resin marker.
Patent Document 1: JP-A-2003-25345